Lymphocyte antigen receptor genes are assembled by a site-specific recombination process, referred to as V(D)J recombination, which is tightly regulated within the context of lymphocyte development. Furthermore, expression of antigen receptor chains is required for appropriate lymphocyte developmental stage progression. Therefore, understanding the mechanistic basis of V(D)J recombination will provide important insights into the molecular basis of lymphocyte development. T-cell receptor (TCR) beta gene rearrangement is ordered during development with D-beta to J-beta rearrangement preceding V-beta to D-beta rearrangement. Furthermore, V-beta to D-beta rearrangement is regulated in the context of allelic exclusion. They have shown that V-beta to D-beta rearrangement is mechanistically coupled through constraints placed on this step by the D-beta recombination signal sequence (RSS) beyond 12/23 compatibility. The goals of the studies described in this proposal are to elucidate the mechanisms responsible for coupling of V-beta to D-beta rearrangement by the 5' D-beta, RSS and to understand their role in regulating the ordered assembly of TCR beta genes during T-cell development. This will be accomplished through three specific aims. 1. Mutational analyses of the 5' D-beta RSS will be conducted to determine the regions responsible for coupling of V-beta to D-beta rearrangement. In addition, they will determine whether coupling by specific RSSs is generalizable to other rearrangement steps. 2. The mechanisms responsible for coupling V-beta to D-beta rearrangement by the 5' D-beta RSS will be elucidated. They will determine whether the requirement for the 5' D-beta RSS is strictly cis-acting. If trans-acting factors are required, they will attempt to isolate these factors. The role of transcriptional initiation, from the TATA box in the 5' D-beta RSS, in coupling V-beta to D-beta rearrangement will be determined. 3. They will determine whether TCR-beta allelic exclusion is accompanied by changes in transcriptional activity, methylation and/or chromatin structure of V-beta gene segments. In addition, the potential mechanistic role of V-beta to D-beta rearrangement coupling in effecting allelic exclusion will be assessed.